Color television screen with correction for overplay



C. W. GEER Feb. 24, 1953 COLOR TELEVISION SCREEN WITH CORRECTION FOROVERPLAY Filed Aug. 4, 1949 Patented Feb. 24, 1953 COLOR TELEVISIONSCREEN WITH CORRECTION FOR OVERPLAY Charles Willard Geer, Long Beach,Calif., assignor to Technicolor Motion Picture Corporation, acorporation of Maine Application August 4, 1949, Serial No. 108,478

(Cl. 313'7ll) 24 Claims.

1 This invention relates to television screens and particularly totelevision screens adapted for the production of color effects inreceiving sets.

An important object of the invention is to fur nish a screen by means ofwhich color efiects may be accurately rendered with clear images.

Another object of the invention is to yield a color television screenwhich will avoid overshooting or overplay of respective electron beamsas they scan the screen, where the screen comprises a multiplicity ofminute pyramids having faces to receive electron beams which arerespectively directed toward the screen from difierent angles, and thefaces upon which the beams impinge are respectively coated withdifferent phosphors adapted to yield different colors upon properenergization by the respective electron beams.

A particular object is to dispose such pyramidal faces at appropriateangles, substantially right angles, to the respective beams at allpositions of such beams as they scan the screen.

The general type of television color screen abovementioned, is disclosedand claimed in my co-pending application, Serial No. 544,384, filed July11, 1944 which issues as United States Letters Patent No. 2,480,848. Itcomprises a carrying surface provided with a multiplicity of trihedralor other pyramids of small sizes below the resolving power of the eye atnormal viewing distances. The surfaces of the trihedrons are arranged inrepeating geometrical patterns with corresponding faces facing in thesame direction, the three series of faces of the trihedrons facingregularly in different directions, the faces of each series facin in agiven direction being coated with a given phosphor which, when energizedby the respective electron beams, is activated to luminescence to yielda given color, which may be one of the primary colors or other principalcolor as desired. Instead of three series of faces, other series such astwo or four may be employed. These series of faces, being coated withphosphors yielding corresponding principal colors when activated, thusgive natural color effects to the observers eye. Such a televisionscreen is disposed within a cathode ray tube or a bulb, often known as akinescope and usually is provided with an electron gun for each seriesof faces, each respective gun being disposed to direct correspondinelectron beams toward the originating in known transmitting apparatusemployed. However, as the beams from the respective guns move whileconventionally scanning the screen, their angle of impingement upon therespective faces constantly varies with respect to.

As a consequence, beams desired to fall only upon a given series offaces tend to overplay or overshoot their respective target faces atvarious parts of the screen and fall obliquely upon portions ofcontiguous phosphor-coated faces which are intended to be energized onlyby electron beams from one of the other guns. Such overshooting oroverplaying of electron beams tends correspondingly to activate thephosphors of other faces at undesired intervals and results incorresponding color confusion of the image to the extent that a truecolor image is not realized unless appropriate correction is made.

It is therefore one object of this invention to provide a pyramidarrangement which corrects such overshooting by varying arrangements ofthe pyramid faces to avoid overshooting or overplaying of respectivebeams in a manner to energize phosphors on other faces not intended tobe energized thereby. I have found that pyramids having appropriateangles at their apexes may be progressively leaned or tipped toward thecentral axis of the screen as the periphery of the screen is approachedby the respective beams so that the respective beams impinge upon therespective pyramidal faces either in approximately perpendicularrelationship, or at least in such relationship, with respect to thetrihedral or other apex angles, that no overplay of the indicated natureW111 occur. Satisfactory arrangements may be attained by employing aconcave surface as the screen support having a curvature to behereinafter described, whereby the increasing curvature toward theperiphery serves automatically to tip the various pyramids whose axesare disposed perpendicular to the respective tangents. One such screensupport may be in the form of a segment of a spherical surface where thedischarge points of the electron guns are disposed approximately at theends of diameters of the semisphere from Which the segment is cutwhereby the angle of impingement between the beams formed by any twoguns is approximately a right angle. Thus, where tetrahedrons areemployed, the angle of impingement between the beams of the two oppositeguns is subtended by a chord which is the diameter at whose ends therespective guns are located. A similar relationship, of course, existsbetween the respective faces of trihedrons and any two of the three gunsused therewith. Similarly, other concaved surfaces may be employed, suchas that wherein the intersection of the concave surface by a planethrough the central axis (a line perpendicular to tangents at thecenter) of the concave support is in the form of the side of minimumcurvature of an ellipse. Thus, one preferred form is that where theminor axis of the ellipse is 0.965 times the distance between the twofoci of the ellipse, the discharge points of the respective guns beinglocated at such foci. In other terms, such an ellipse is that whereinthe eccentricity of the ellipse (the ratio of the distance between thefoci to the major axis) is about 0.72.

Other appropriate curvatures, other objects of the invention, and thevarious features of the invention will become apparent to those skilledin the art upon reference to the following description and theaccompanying drawing wherein certain embodiments of the invention aredisclosed.

In the drawing:

Fig. 1 is principally a side elevation of a television bulb of thekinescope type within which an improved color screen of the presentinvention is located, a portion of the bulb being broken away toindicate the screen relationship, three electron guns being present;

Fig. 2 is a front elevation of the bulb of Fig. 1 as indicated by theline 22 of Fig. 1;

Fig. 3 is a front elevation of a bulb employing four electron guns;

Fig. 4 is a fragmentary elevation of the inner face of the screen, asindicated by the arrow 4 of Fig. l, where the pyramids are of trihedralconstruction;

Fig. 5 is a similar fragmentary elevation of the inner face of thescreen of Fig. 3 where the pyramids are of tetrahedral construction andfour electron guns are used;

Fig. 6 is a diagrammatic view representing the relationships between theelectron guns and the pyramids on the screen approximately as indicatedon the line B6 of Fig. 2 where three electron guns are employed, and asrepresented by a straight diameter 66 in Fig. 3 where four electron gunsare employed; and

Fig. '7 is a fragmentary diagrammatic radial section taken on a screendiameter to represent the progressive tipping of the pyramids toward thecenter of the screen as the pyramids lie farther radially outward towardthe periphery of the screen,

Having further reference to the drawing, Fig. 1 illustrates an evacuatedglass, cathode-ray tube or bulb ID of the kinescope type having at itsfront a concave viewing screen [2, its rearward portion being providedwith three electron guns l4, l5, and I6 arranged 120 apart as indicatedin Fig. 2. A similar structure is shown in Fig. 3 except that a fourthelectron gun I! is used in order to provide for four principal colors.The various electron guns are carried by integral necks l8, and thesenecks are so mounted with respect to the screen l2 as to direct beamsfrom the respective guns toward the trihedral or tetrahedral pyramids atangles approximating 45 to the general plane of the screen l2, which isparallel to a plane tangent to the central point of the screen and tothe elevation line 2-2. Thus, the guns of Figs. 1 and 2 are not onlyarranged- 4 at angles of 120 to each other but are also tipped towardthe screen [2 at angles of about 45. Similarly adjacent guns of Fig. 3are arranged at to each other, these guns also being tipped with respectto the screen at angles of about 45.

As to manipulation of the electron guns I4, [5, l6, and IT to scan thescreen I2, this will be controlled by means well understood in thetelevision art. Similarly, the employment of analyzing equipment tosegregate and present color signals in proper frequencies to therespective electron guns in correspondence with the natural colors ofthe image being televised is likewise known in the art. Therefore,explanation and description of such aspects, which are no part of thepresent invention, are not presented here.

Where three electron guns and trihedral, pyramidal screen elements areemployed, as in Figs. 1, 2, and 4, the three exposed faces of thetrihedrons are provided with three different phosphors to yielddifferent cathodo-luminescences representing desired principal colorssuch as red, blue, and green, and Where four electron guns andtetrahedral, pyramidal screen elements are required, as in Figs. 3 and5, four phosphors yielding different cathodo-luminescences will beemployed to provide desired colors.

In general, the pyramids of Figs. 4 and 5 are indicated at 20,regardless of whether they are trihedral or tetradedral, and in the caseof the trihedral pyramids of Fig. 4, the corresponding three faces arerespectively indicated at 2|, 22, and 23, and in the case of thetetrahedral pyramids of Fig. 5, the corresponding four faces arerepresepted at 24, 25, 25, and 21.

The pyramidal screen elements 20 are mounted upon the inner face of ascreen wall 30 (Figs. 1 and '7) which is formed from appropriatetransparent or translucent material, such as glass, plastic, or thelike. The pyramids 20 may be integral with such transparent ortranslucent material, or they may be separately produced and attachedthereto as required. The screen elements may be shaped by appropriateruling or engraving upon an appropriately curved master form or die, orupon a corresponding flat memher, the screen structure being finallyshaped in any desired manner, such as against a properly curved moldunder conditions providing suflicient softening for the production ofthe required curvature.

According to an improvement of this invention, the curvature of thescreen I2 is such with respect to the points of electron emission fromthe various electron guns that the electron beams, as they scan thescreen, will always fall approximately perpendicularly upon therespective faces of the pyramidal elements 20. As viewed in Figs. 6 and'7, this is accomplished by reason of the fact that the curvature of thescreen causes the various pyramidal elements 20 to tip toward thecentral axis of the screen, which, as viewed in Figs. 6 and 7, is avertical line rising perpendicularly from the lowermost point of thescreen and therefore being perpendicular to the plane tangent to thecenter of the screen. Such tangent plane is indicated by the line 35 inFigs. 6 and '7 and such central perpendicular axis is indicated by theline 36.

As illustrated in Fig. 6, a perforated form of curvature for the concavescreen, at each diameter, is represented by the side of minimumcurvature of an ellipse of such construction that where the emissionpoints of the corresponding electron guns are placed at the foci, thebeams from such guns fall approximately perpendicularly upon therespective pyramidal faces as the beams move during their scanningoperations. A suitable ellipse may be determined in either of twomanners. In the first, the minor axis of the ellipse is to beapproximately 0.965 times the distance between the foci which areindicated at F1 and F2 in Fig. 6, these relative positions being alsoindicated by the same reference characters in Figs. 1, 2, and 3. Such anellipse may also be established by providing an eccentricity of about0.72, this eccentricity being the ratio of the distance between the fociF1 and F2 to the major axis of the ellipse which is the distance betweenthe points indicated at A and B in Fig. 6. The minor axis abovementioned is the line extending between the points C and D in Fig. 6located at the opposite sides of the ellipse. Such an elliptical curveis indicated at 38.

Another appropriate concavity for the screen l2 and its support 36 is ashallow segment of a sphere whose radius approximates the minor axis CDof the above mentioned ellipse of Fig. 6 and where the emission pointsof the corresponding electron guns are to be disposed at the fooi ofsuch ellipse, such a curve being indicated at All. Possibly such a curvewith a radiu equal to FiFz would be useful in many instances, its centerthus being at E in Fig. 6. However, an arcuate curve having a radiusapproximating or between /3 and 9 10, of said minor axis, apparently isa preferable curvature, the latter curve being indicated at 42 andhaving its center at 62c. In this case, the emission points of the gunswould be at the points F1 and F2, or approximately at these points. Sucha curve may be otherwise described as having a radius (D420) which isapproximately of the radius (DC) of a larger circle in whose semicirclea square (approximately DF1CF2) may be inscribed, one of whose diagonals(DC) is the radius of the larger circle, the ends of the other diagonalof the square defining approximately the loci of the emission points ofthe respective electron guns. Thus, these emission points will be at orclose to the points F1 and F2. Another appropriate curvature would beany compromise between the elliptical curve 38 and the arcuate curve 49.

Again, a shallow segment of a sphere formed with any radius may beemployed where the discharge points of the respective electron guns areto be disposed at the outer ends of opposing radii or of the respectivediameter, such as indicated at 43 and it, whereby the angle ofimpingement between beams from the guns, being subtended by suchdiameter, is necessarily 90. These relationships are, of course, thoseexisting as viewed in the respective plane in which the axes of any twogiven guns lie, whether on a straight diameter with four guns andtetrahedrons, as indicated by the line 6-6 of Fig. 3, or on a differentplane as indicated by the line 8-8 of Fig. 2 representing three guns andtrihedrons.

Under all of these circumstances it will be apparent that the apexangles of the pyramids approximate 90 as between any two faces andconsequently provide proper correction regardless of whether three orfour guns with corresponding trihedrons or tetrahedrons are employed.Relative portions of the concave members to be used as a screen withrespect to the various curves mentioned may lie approximately betweenthe short vertical lines 45 and 46 indicated in the lower portion ofFig. 6.

As will be apparent from the showing of the drawing and the'abovedescriptive matter, the pyramids of the screen, whether they betrihedrons or tetrahedrons, present a plurality of series of faces, theface of each series being faced generally in the same direction wherebyto receive electron beams from the respective guns, and the axes of thepyramids are tipped inward toward the central axis of the screen, thistipping increasing progressively with respect to the plane of referencerepresented by the line 35 of Fig. 6 as respective pyramids lie radiallyfarther out from the screen center. Any such error as exists in anyscreen whose diameters are constructed as described will be small, andthis error can be easily corrected by correspondingly reducing thetrihedral or tetrahedral angle below the axis of the respective pyramidbeing directed so as to bisect the angle formed between the tworespective electron beams impinging on such pyramid.

Since modifications of the generic invention herein disclosed will occurto those skilled in this art, it is intended to protect all variationswhich fall within the scope of the patent claims.

I claim as my invention:

1. A television screen for overplay correction and comprising: asupporting surface; and a multiplicity of pyramids on said surface, eachof which presents a plurality of impingement faces for electron beams ofa corresponding plurality of electron guns, each face of each pyramidbeing directed in substantially the same direction as correspondingfaces of all the other pyramids and forming therewith a correspondingplurality of series of faces, each series carrying a given phosphoractivatable by respective electron beams to yield a given principalcolor, pyramids at the center of the screen having their axesperpendicular to the corresponding screen portion, the axes of thepyramids outside said center being progressively tipped increasinglytoward the screen center of the screen as the pyramids lie progressivelyfarther outward from said screen center, whereby to dispose therespective faces in planes substantially perpendicular to the respectivebeams and thereby to compensate for angular change of direction of therespective electron beams as the respective guns scan said screen.

2. A television screen for overplay correction and comprising: asupporting surface; and a multiplicity of pyramids carried on saidsurface, each of which presents a plurality of impingement faces forelectron beams of a corresponding plurality of electron guns, each faceof each pyramid being directed in substantially the same direction ascorresponding faces of all the other pyramids and forming therewith acorresponding plurality of series of faces, each series carrying a givenphosphor activatable by respective electron beams to yield a givenprincipal color, said surface carrying said pyramids possessingconcavity and said pyramids having their pyramidal axes approximatelyperpendicular to tangents at their respective points of ourvaturewhereby pyramids disposed radially outward from the screen center areprogressively tipped toward said screen center as the pyramids lieprogressively further outward from the screen center to dispose therespective faces in planes substantially perpendicular to the respectivebeams and thereby to compensate for angular change of direction of therespective electron aoaasae beams as the respective guns scan saidscreen.

3. A television screen for overplay correction and comprising: asupporting surface; and a multiplicity of pyramids carried on saidsurface, each of which presents a plurality of impingement faces forelectron beams of a corresponding plurality of electron guns, each faceof each pyramid being directed in substantially the same direction ascorresponding faces of all the other pyramids and forming therewith acorresponding plurality of series of faces, each series carrying a givenphosphor activatable by respective electron beams to yield a givenprincipal color, said surface carrying said pyramids possessingconcavity and said pyramids having their pyramidal axes approximatelyperpendicular to tangents at their respective points of curvaturewhereby pyramids disposed radially outward from the screen center areprogressively tipped toward said screen center as the pyramids lieprogressively further outward from the screen center to dispose therespective faces in planes substantially perpendicular to the respectivebeams and thereby to compensate for angular change of direction of therespective electron beams as the respective guns scan said screen, thecurvature of the said surface being the surface of a segment of aspherewithin whose outer limits the discharge points of said guns are to belocated.

4. A television screen for overplay correction and comprising: asupporting surface; and a multiplicity of pyramids carried on saidsurface, each of which presents a plurality of impingement faces forelectron beams of a corresponding plurality of electron guns, each faceof each pyramid being directed in substantially the direction ascorresponding faces of all the other pyramids and forming therewith acorresponding plurality of series of faces, each series carry- 4 ing agiven phosphor activatable by respective electron beams to yield a givenprincipal color, said surface carrying said pyramids possessingconcavity and said pyramids having their pyramidal axes approximatelyperpendicular to tangents at their respective points of curvaturewhereby pyramids disposed radially outward from the screen center areprogressively tipped toward said screen center as the pyramids lieprogressively further outward from the screen center to dispose therespective faces in planes substantially perpendicular to the respectivebeams and thereby to compensate for angular change of direction of therespective electron beams as the respective guns scan said screen, thecurvature of the said surface being the surface of a segment of a spherewithin whose outer limits the discharge points of said guns are to belocated, the radii of said sphere being approximately equal to twice thedistance between a gun discharge point and the perpendicular to thecenter of the screen.

5. A television screen for overplay correction and comprising: asupporting surface; and a multiplicity of pyramids carried on saidsurface, each of which presents a plurality of impingement faces forelectron beams of a corresponding plurality of electron guns, each faceof each pyramid being directed in substantially the same direction ascorresponding faces of all the other pyramids and forming therewith acorresponding plurality of series of faces, each series carrying a givenphosphor activatable by respective electron beams to yield a givenprincipal color, said surface carrying said pyramids possessingconcavity and said pyramids having their pyramidal axes approximatelyperpendicular to tangents at their respective points of ourvaturewhereby pyramids disposed radially outward from the screen center areprogressively tipped toward said screen center as the pyramids lieprogressively further outward from the screen center to dispose therespective faces in planes substantially perpendicular to the respectivebeams and thereby to compensate for angular change of direction of therespective electron beams as the respective guns scan said screen, thecurvature of the said surface being such that each diameter of saidconcavity is formed on the side of minimum curvature of an ellipse whosefoci constitute the locus of the discharge points of the guns and thelength of whose minor axis approximates the distance between said foci.

6. A television screen for overplay correction and comprising: asupporting surface; and a multiplicity of pyramids carried on saidsurface, each of which presents a plurality of impingement faces forelectron beams of a corresponding plurality of electron guns, each faceof each pyramid being directed in substantially the same direction ascorresponding faces of all the other pyramids and forming therewith acorresponding plurality of series of faces, each series carrying a givenphosphor activatable by respective ectron beams to yield a givenprincipal color, said surface carrying said pyramids possessingconcavity and said pyramids having their pyramidal axes approximatelyperpendicular to tangents at their respective points of curvaturewhereby pyramids disposed radially outward from the screen center areprogressively tipped toward said screen center as the pyramids lieprogressively further outward from the screen center to dispose therespective faces in planes substantially perpendicular to the respectivebeams and thereby to compensate for angular change of direction of therespective electron beams as the respective guns scan said screen, thecurvature of the said surface being such that each diameter of saidconcavity is formed on the side of minimum curvature of an ellipse whosefoci constitute the locus of the discharge points of the guns and thelength of whose minor axis is about 0.965 times the distance betweensaid foci.

7. A television tube comprising in combination: a screen at one end ofsaid tube; a multiplicity of pyramids on said screen, each pyramidpresenting a plurality of impingement faces, corresponding faces of thepyramids being faced generally in the same direction and constituting acorresponding plurality of series of faces, each series of facescarrying a phosphor yielding a different color upon energization fromthat of each other ccries of faces; and a plurality of electron gunscarried by said tube and corresponding in number with the number of saidseries of faces, said guns being directed angularly toward therespective series of faces from points spaced from said screen, pyramidsat the center of the screen having their axes substantiallyperpendicular to the plane of the corresponding screen portion, and theaxes of the pyramids beyond the center of the screen being tipped towardsaid center, the degree of tipping increasing progressively as thepyramids lie progressively farther outward from the screen center,whereby to compensate for change in angularity of beams from said gunsas they scan said screen.

8. A television tube comprising in combination: a screen at one end ofsaid tube; a multiplicity of pyramids on said screen, each pyramidpresenting a plurality of impingement faces, corresponding faces of thepyramids being faced generally in the same direction and constituting acorresponding plurality of series of faces, each series of facescarrying a phosphor yielding a different color upon energization fromthat of each other series of faces; and a plurality of electron gunscarried by said tube and corresponding in number with the number of saidseries of faces, said guns being directed angularly toward therespective series of faces from points spaced from said screen, saidscreen possessing concavity and said pyramids having their axesapproximately perpendicular to tangents at their corresponding screenportions whereby pyramids disposed radially outward from the screencenter are tipped toward said center, the degree of tipping increasingprogressively as the pyramids lie progressively further outward from thescreen center to compensate for change in angularity of beams from saidguns as they scan said screen.

9. A television tube comprising in combination: a bulb; a concave screenat one end of said bulb; a multiplicity of pyramids on said screen, eachpyramid presenting a plurality of impingement faces, corresponding facesof the pyramids being faced generally in the same direction andconstituting a corresponding plurality of series of faces, each seriesof faces carrying a phosphor yielding a different color from that ofeach other series of faces upon energization, pyramids at the center ofthe screen having their axes substantially perpendicular to the plane ofthe screen as a whole, and the curvature of the concavity of the screenon each radius causing the axes of the pyramids beyond the center of thescreen to be tipped toward said center, the degree of tippingprogressively increasing by reason of said curvature as the pyramids lieprogressively farther outward from the screen center; a plurality ofelectron guns carried by said tube adjacent its end opposite from saidscreen and corresponding in number with the number of said series offaces, said guns being directed angularly toward the respective facesfrom points spaced from said screen, the curvature of said concavescreen whereby said tipping is effected serving to compensate for changein angularity of electron beams from said guns as they scan said screen.

10. A television tube comprising in combination: a bulb: a concavescreen at one end of said bulb; a multiplicity of pyramids on saidscreen, each pyramid presenting a plurality of impingement faces,corresponding faces of the pyramids being faced generally in the samedirection and constituting a corresponding plurality of series of faces,each series of faces carrying a phosphor yielding a different color fromthat of each other series of faces upon energization, pyramids at thecenter of the screen having their axes substantially perpendicular tothe plane of the screen as a whole, and the curvature of the concavityof the screen on each radius causing the axes of the pyramid-s beyondthe center of the screen to be tipped toward said center, the degree oftipping progressively increasing by reason of said curvature as thepyramids lie progressively farther outward from the screen center; aplurality of electron guns carried by said tube adjacent its endopposite from said screen and corresponding in number with the number ofsaid series of faces,

said guns being directed angularly toward the respective faces frompoints spaced from said screen, the curvature of said concave screenbeing such that each diameter of said screen is formed on the side ofminimum curvature of an ellipse within whose confines the emissionpoints of the respective electron guns are located.

11. A television tube comprising in combination: a bulb; a concavescreen at one end of said bulb; a multiplicity of pyramids on saidscreen, each pyramid presenting a plurality of impingement faces,corresponding faces of the pyramids being faced generally in the samedirection and constituting a corresponding plurality of series of faces,each series of faces carrying a phosphor yielding a different color fromthat of each other series of faces upon energization, pyramids at thecenter of the screen having their axes substantially perpendicular tothe plane of the screen as a whole, and the curvature of the concavityof the screen on each. radius causing the axes ofv the pyramids beyondthe center of the screen to be tipped toward said center, the degree oftipping progressively increasing by reason of said curvature as thepyramids lie progressively farther outward from the screen center; aplurality of electron guns carried by said tub-e adjacent its endopposite from said screen and corresponding in number with the number ofsaid series of faces, said guns being directed angularly toward therespective facesirom points spaced from said screen, the curvature ofsaid concave screen being such that each diameter of said screen isformed on the side of minimum curvature of an ellipse, the foci of saidellipse constituting the locations of the emission points of therespective guns, and the length of the minor axis of said ellipseapproximating the distance between said foci.

12. A television tube comprising in combination: a bulb; a concavescreen at one end of said bulb; a multiplicity of pyramids on saidscreen, each pyramid presenting a plurality of impingement faces,corresponding faces of the pyramids being faced generally in the samedirection and constituting a corresponding plurality of series of faces,each series of faces carrying a phosphor yielding a different color fromthat of each other series of faces upon energization, pyramids at thecenter of the screen having their axes substantially perpendicular tothe plane of the screen as a whole, and the curvature of the concavityof the screen on each radius causing the axes of the pyramids beyond thecenter of the screen to be tipped toward said center, the degree oftipping progressively increasing by reason of said curvature as thepyramids lie progressively farther outward from the screen center; aplurality of electron guns carried by said tube adjacent its endopposite from said screen and corresponding in number with the number ofsaid series of faces, said guns being directed angularly toward I therespective faces from points spaced from said screen, the curvature ofsaid concave screen being such that each diameter of said screen isformed on the side of minimum curvature of an ellipse, the foci of saidellipse constituting the locations of the emission points of therespective guns, and the length of the minor axis of said ellipse being0.965 times the distance between said foci.

13. A television tube comprising in combination: a bulb; a concavescreen at one end of said bulb; a multiplicity of pyramids on saidscreen, each pyramid presenting a plurality of impingement faces,corresponding faces of the pyramids 11 being faced generally in the samedirection and constituting a corresponding plurality of series of faces,each series of faces carrying a phosphor yielding a different color fromthat of each other series of faces upon energization, pyramids at thecenter of the screen having their axes substantially perpendicular tothe plane of the screen as a whole, and the curvature of the concavityof the screen on each radius causing the axes of the pyramids beyond thecenter of the screen to be tipped toward said center, the degree oftipping progressively increasing by reason of said curvature as thepyramids lie progressively farther outward from the screen center; aplurality of electron guns carried by said tube adjacent its endopposite from said screen and corresponding in number with the number ofsaid series of faces, said guns being directed angularly toward therespective faces from points spaced fromv said screen, the curvature ofsaid concave screen being such that each diameter of said screen is,formed on the side of, minimum curvature of an ellipse having aneccentricity of about 0.72, and the emission points of the respectiveelectron guns being located approximately at the foci of said ellipse.

14. A television tube comprising in combination: a bulb; a concavescreen at one end of said bulb; a multiplicity of pyramids on saidscreen, each pyramid presenting a pluralityof impingement faces,corresponding faces ofthe-pyramids being faced generally in the samedirection and constituting a corresponding plurality of series of faces,each series of faces carrying a phosphor yielding a different color fromthat of each other series of faces upon energization, pyramids at thecenter of the screen having their axes substantially perpendicular tothe plane of the screen as a whole, and the curvature of the concavityof the screen on each radius causing the axes of the pyramids beyond thecenter of the screen to be tipped toward said center, the degree oftipping progressively increasing by reason of said curvature as thepyramids lie progressively farther outward from the screen center; aplurality of electron guns carried by said tube adjacent its endopposite from said screen and corresponding in number with the number ofsaid series of faces, said guns being directed angularly toward therespective faces from points spaced from said screen, said concavescreen being the surface of a shallow segment of a sphere within the.limits of which the emission points of said guns are located.

15,, A. television tube comprising in combination: .a bulb; a concave.screen at one end of said bulb; a multiplicity of pyramids on saidscreen, each pyramid presenting a plurality of impingement faces,corresponding faces of the pyramids being faced generally in the samedirection and constituting a corresponding plurality of series of faces,each series of faces carrying a phosphor yielding a different color fromthat of each other series of faces upon energization, pyramids at thecenter of the screen having their axes substantially perpendicular tothe plane of the screen as a whole, and the curvature of the concavityof the screen on each radius causing the axes of the pyramids beyond thecenter of the screen to be tipped toward said center, the degree oftipping progressively increasing by reason of said curvature as thepyramids lie progressively farther outward from the screen center; aplurality of electron guns carried by said tube adjacent its end.opposite from said screen and correspondingin number with the number ofsaid series of faces, said guns being directed angularly toward therespective faces from points spaced from said screen, said concavescreen being the surface of a shallow segment of a sphere within thelimits of which the emission points of said guns are located, the radiusof said sphere being approximately equal to twice the distance between agun emission point and the central axis of said screen.

16. A television tube comprising in combination: a bulb; a concavescreen at one end of said bulb; a multiplicity of pyramids on saidscreen, each pyramid presenting a plurality of impingement faces,corresponding faces of the pyramids being faced generally in the samedirection and constituting a corresponding plurality of series of faces,each series of faces carrying a phosphor yielding'a different color fromthat of each other series offaces upon energization, pyramids at thecenter of the screen having their axes substantially perpendicular tothe plane of the screen as a whole, and the curvature of the concavityof the screen on each radius causing the axes of the pyramids beyond thecenter of the screen to be tipped toward said center, the degree oftipping progressively increasing by reason of said curvature as thepyramids lie progressively'farther outward from the screen center; aplurality of electron guns carried by said tube adjacent its endopposite from said screen and corresponding in number with the number ofsaid series of faces, said guns being directed angularly toward therespective faces from points spaced from said screen, and the faces ofsaid pyramids being exposed at angles of approximately with respect tothe respective beams projected by the respective electron guns.

17. A television tube comprising in combination: a bulb; a concavescreen at one end of said bulb; a multiplicity of pyramids on saidscreen, each pyramid presenting a plurality of impingement faces,corresponding faces of the pyramids being faced generally in the samedirection and constituting a corresponding plurality of series of faces,each series of faces carrying a phosphor yielding a different color fromthat of each other series of faces upon energization, pyramids at thecenter of the screen having their axes substantially perpendicular tothe plane of the screen as a whole, and the curvature of the concavityof the screen on each radius causing the axes of the pyramids beyond thecenter of the screen to be tipped toward said center, the degree. oftipping progressively increasing by reason of said curvature as thepyramids lie progressively farther outward from the screen center; aplurality of electron guns carried by said tube adjacent its endopposite from said screen and corresponding in number with the number ofsaid series of faces, said guns being directed angularly toward therespective faces from points spaced from said screen, the curvature ofsaid screen being such that each diameter of said concavity is in theform of a shallow segment of a circle whose radius approximateseight-ninths of the radius of a larger circle within whose semi-circle asquare may be inscribed, one of whose diagonals is approximately aradius of the larger circle, the ends of its other diagonal beingapproximately the loci of the emission points of the respective electronguns.

18. A television tube comprising in combination: a bulb; a concavescreen at one end of said bulb; a multiplicity of pyramids on saidscreen,

each pyramid presenting a plurality of impingement faces, correspondingfaces of the pyramids being faced generally in the same direction andconstituting a corresponding plurality of series of faces, each seriesof faces carrying a phosphor yielding a different color from that ofeach other series of faces upon energization, pyramids at the center ofthe screen having their axes substantially perpendicular to the plane ofthe screen as a whole, and the curvature of the concavity of the screenon each radius causing the axes of the pyramids beyond the center of thescreen to be tipped toward said center, the degree of tippingprogressively increasing by reason of said curvature as the pyramids lieprogressively farther outward from the screen center; a plurality ofelectron guns carried by said tube adjacent its end opposite from saidscreen and corresponding in number with the number of said series offaces, said guns being directed angulariy toward the respective facesfrom points spaced from said screen, the curvature of said concavescreen whereby said tipping is effected serving to compensate for changein angularity of electron beams from said guns as they scan said screen,each diameter of said concavity being formed on a curve which is acompromise between a side of minimum curvature of ellipse whose fociconstitute the loci of the emission points of the electron guns and thelength or whose minor axis approximates 0.965 times the distance betweensaid ioci, and a shallow segment of a circle whose radius approximateseight-ninths of the radius of a larger circle radius approximately equalto the minor axis of said ellipse, such minor axis and larger circleradius constituting one diagonal of a square, the ends of whose otherdiagonal define approximately the loci of the emission points of therespective electron guns.

19. A color television tube of the class described, including a concavescreen, the curvature of which lies between a side of minimum curvatureof an ellipse and a segment of a semi-circle Whose radius approximatesthe minor axis of the said ellipse.

2D. A color television tube of the class described, including a concavescreen, the curvature of which lies between a side of minimum curvatureof an ellipse and a segment of a semicircle whose radius approximatesbetween and of the minor axis of the said ellipse.

21. A color television tube of the class described, including a concavescreen, the curvature of which lies between a side of minimum curvatureof an ellipse and a segment of a semi-circle whose radius approximatesthe minor axis of the said ellipse and electron guns, the dischargepoints of which are disposed within the said semi-circle.

22. A color television tube of the class described, including a concavescreen, the curvature of which lies between a side of minimum curvatureof an ellipse and a segment of a semicircle whose radius approximatesbetween V and of the minor axis of the said ellipse and electron guns,the discharge points of which are disposed within the said semi-circle.

23. A color television tube of the class described, including a concavescreen, the curvature of which lies between a side of minimum curvatureof an ellipse and a segment of a semi-circle whose radius approximatesthe minor axis of the said ellipse and electron guns, the dischargepoints of which are disposed at the foci of the said ellipse.

24. A color television tube of the class described, including a concavescreen, the curvature of which lies between a side of minimum curvatureof an ellipse and a segment of a semi-circle whose radius approximatesbetween '78 and of the minor axis of the said ellipse and electron guns,the discharge points of which are disposed at the foci of the saidellipse.

CHARLES WILLARD GEER.

REFERENGES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,603,28l Johnson Oct. 19, 19262,089,546 Dudding et al Aug. 10, 1937 2,151,992 Schwartz Mar. 28, 19392,254,090 Power Aug. 26, 1941 2357.175 Parker Dec. 28, 1948 2,%80,8l8Greer Sept. 6, 1949 2,481,839 Goldsmith Sept. 13, 1949 FOREIGN PATENTSNumber Country Date 562,168 Great Britain June 21, 1944

